The present invention relates to an operation mode switching mechanism for a hammer drill equipped with a striking force transmitting mechanism and a rotational force transmitting mechanism.
According to a conventional operation mode switching mechanism of a hammer drill, the striking force transmitting mechanism is provided around a crank shaft while the rotational force transmitting mechanism is provided around a tool shaft.
This arrangement is disadvantageous in that the longitudinal tool length becomes long and a peripheral or surrounding portion of the tool shaft cannot be downsized due to provision of the rotational force transmitting mechanism.
An object of the present invention is to provide a hammer drill having a short axial length as well as capable of realizing excellent operability with at least three operation modes.
In order to accomplish this and other related objects, the present invention provides a hammer drill comprising a motor rotating a drive shaft, an external frame member accommodating the motor therein, a first gear having a claw portion and engaged with the drive shaft for transmitting the rotation of the drive shaft, and a second gear having a claw portion and engaged with the drive shaft for transmitting the rotation of the drive shaft. The first and second gears are positioned in parallel with each other. A first switching member has a claw portion engageable with the claw portion of the first gear for transmitting the rotation of the drive shaft when the claw portion of first switching member is engaged with the claw portion of the first gear. A crank shaft is driven in response to the rotation of the first switching member. A striking force transmitting mechanism, responsive to the rotation of the crank shaft, transmits a reciprocative striking force to a tool bit. A second switching member having a claw portion engageable with the claw portion of the second gear for transmitting the rotation of the drive shaft when the claw portion of second switching member is engaged with the claw portion of the second gear. An intermediate shaft is driven in response to the rotation of the second switching member. A rotational force transmitting mechanism, responsive to the rotation of the intermediate shaft, transmits a rotational force to the tool bit. And, a switching lever selectively engages or disengages the claw portion of first switching member with or from the claw portion of the first gear and also selectively engages or disengages the claw portion of second switching member with or from the claw portion of the second gear.
According to a preferable embodiment of this invention, the first gear is rotatably mounted on the crank shaft, the first switching member is mounted on the crank shaft so as to be slidable in an axial direction of the crank shaft without causing any relative rotation therebetween, the second gear is rotatably mounted on the intermediate shaft, and the second switching member is mounted on the intermediate shaft so as to be slidable in an axial direction of the intermediate shaft without causing any relative rotation therebetween.
According to the preferable embodiment of this invention, a first urging member resiliently urges the first switching member so that the claw portion of the first switching member is engaged with the claw portion of the first gear, and a second urging member resiliently urges the second switching member so that the claw portion of the second switching member is engaged with the claw portion of the second gear.
According to the preferable embodiment of this invention, the switching lever is rotatably supported on the external frame member so that the first switching member can shift in the axial direction of the crank shaft and the second switching member can shift in the axial direction of the intermediate shaft.
According to the preferable embodiment of this invention, the second switching member has a toothed portion that is engageable with a toothed portion of a rotation restricting member, and the rotation restricting member is provided inside the external frame member so as not to cause any relative rotation therebetween.
According to the preferable embodiment of this invention, the claw portion of the second switching member is engaged with the claw portion of the second gear when the second switching member is positioned at a first position. The claw portion of the second switching member is disengaged from the claw portion of the second gear when the second switching member is positioned at a second position. And, the claw portion of the second switching member is selectively engaged with or disengaged from the toothed portion of the rotation restricting member when the second switching member is positioned at the second position.
According to the preferable embodiment of this invention, a switching assist shaft is provided so as to extend in parallel with the crank shaft and the intermediate shaft, and a shift member is provided on the switching assist shaft so as to be slidable in the axial direction without causing any relative rotation therebetween, the shift member being engageable with the first switching member or the second switching member so as to shift the first switching member in the axial direction of the crank shaft or shift the second switching member in the axial direction of the intermediate shaft.
According to the preferable embodiment of this invention, the switching lever has a first eccentric pin engageable with the first or second switching member to shift the first or second switching member in the axial direction in response to the rotation of the switch lever, and a second eccentric pin engageable with the shift member to shift the shift member in the axial direction in response to the rotation of the switch lever.